proto marshal to json enumber as string

默认情况下，将生成的pb struct marshal 后生成的json中，枚举值是整型。如何将枚举值编程string 呢用jsonpb，注意枚举值0 会被omitempty掉

https://github.com/golang/protobuf

var msg bytes.Buffer

m := jsonpb.Marshaler{}
err := m.Marshal(&msg, event)

https://stackoverflow.com/questions/49962893/converting-protobuf3-with-enum-to-json-in-go

https://pkg.go.dev/github.com/golang/protobuf/jsonpb#Marshaler.Marshal

https://github.com/golang/protobuf

https://seb-nyberg.medium.com/customizing-protobuf-json-serialization-in-golang-6c58b5890356

https://github.com/gogo/protobuf/blob/master/extensions.md

https://github.com/grpc-ecosystem/grpc-gateway/issues/1063

https://github.com/drslump/ProtoJson

https://github.com/protocolbuffers/protobuf-go

https://github.com/ludiosarchive/Protojson